The present invention relates to an apparatus making it possible to continuously adjust the stroke of the piston of a jack, usable more particularly in the case of a differential piston.
At present, various apparatus types exist which make it possible to modify the length of a piston stroke. For example, U.S. Pat. No. 2,898,890 describes such an apparatus in which compressed air can be blown into each of the ends of a cylinder within which displacement of the piston takes place. A plurality of discharge ports, sealed by valves, are distributed along the cylinder. The opening of one of these valves leads to a pressure drop on one side of the piston and, due to an appropriate system, the compressed air is despatched from the other side of the piston, which then moves back level with the selected port. In this way, a rough adjustment of the piston stroke is obtained by choosing the discharge port. However, this apparatus has a certain number of disadvantages. Firstly, it does not permit a continuous variation of the displacement amplitude. In addition, the installation is relatively complex and therefore costly, because there are a large number of discharge ports and each of the closing valves is controlled by a solenoid.